This invention relates to masts and methods for erecting masts, and more particularly to masts and methods of erecting masts on offshore drilling platforms or at remote land sites.
Different types of masts have been devised for use in drilling and workover of oil wells. In many applications, it is desirable for such masts to be portable from one well to the next, especially in offshore or remote area drilling. To meet this need, it has been the practice to make masts in telescoping sections which sections can then be extended one above the other to make a mast the desirable height.
Well known in the art are two section telescoping masts wherein the upper section is telescoped into the lower section and the entire assembly is transported from one location to the next. Such masts are transported horizontally to the erection site and the collapsed assembly is jackknifed into vertical position at which time the upper section is fully extended. A second type of portable mast involves the use of a three section mast where the intermediate section is telescoped within the lower section and the upper section is telescoped within the intermediate section. During transport from one location to the next, this type of mast is carried horizontally in collapsed form and upon arrival at a new location the collapsed mast is raised to a vertical position and fastened to a substructure. The upper and intermediate sections are then extended and fastened together to form a complete mast.
One problem typically encountered in offshore or remote area drilling is that only small capacity cranes are available for mast erection. In some instances cranes capable of handling only modest loads, on the order of 8,000 lbs., and capable of working at relatively low heights are available. Mast structures which telescope into a single assembly can exceed the weight and size limitations of the crane.
The most practical mast structure in offshore or remote area operations is one constructed of three separate sections of relatively modest size and weight. A mast formed of three separate modules provides a load which a small capacity crane can handle efficiently and an extended mast sufficiently tall to perform workover and drilling operations.
Multiple section modular masts are known in the art, but those currently in use are not easily erected on offshore platforms or at remote land sites. Some of these masts are only semimodular, one section is transported within the lower section and the third section is inserted within an opening in the lower section. Others require a more elaborate erection procedure such as jackknifing and in some, the height of the upper section which is inserted into openings in the lower section is severely limited.
Accordingly, a need arises for an improved vertically extensible telescoping mast having at least three separate sections each of which can be handled by a small capacity crane.